The present invention relates to a stable latex useful for increasing the viscosity of water and for the enhanced recovery of subterranean oil.
Enhanced oil recovery is typically carried out by flushing the oil-containing subterranean formations with a fluid capable of displacing the oil in the formation. This fluid is injected into the formation through at least one injection well so as to drive the oil through the formation to at least one production well. Fluids useful for enhanced oil recovery may either be a liquid or a gas with the most economical and widely used fluid being water. The major drawback with water is that it does not displace the petroleum efficiently since it is not immiscible with oil and because the interfacial tension between oil and water is quite high. The result is that the water will generally move past the oil to a more permeable area of the formation leaving behind substantial quantities of residue oil in the oil-bearing formations.
Various means have been developed to reduce the interfacial tension between the water and oil. This generally involves admixing various types of surfactants with water.
Typical surfactants, which have been used to reduce the interfacial tension between the water and the oil in subterranean formations, are the various types of sulfates and sulfonates, such as petroleum sulfates and sulfonates.
It is also generally desirable to provide the water with a viscosity greater than that of the oil present in the subterranean formation to increase the effectiveness of water in displacing the oil. The viscosity of the water may be increased by preparing aqueous emulsions or dispersions having a dispersed hydrocarbon phase, by dispersing a hydrocarbon, for example crude oil or distilled fractions of crude oil into water using surfactants such as the sulfonates or sulfates.
It is also known that the viscosity of water may be increased by preparing aqueous solutions or emulsions of certain types of polymers. Typically, a concentrated composition of these polymers is prepared which can be blended with water at the well site to increase the viscosity of the water prior to injection into the subterranean formation. U.S. Pat. No. 3,909,423 discloses a composition of polyacrylamides, polymethacrylamides, and water wherein a portion of the carboxyamide group has been hydrolyzed to form carboxyl groups which can then be cross linked so as to increase the viscosity of the water.
U.S. Pat. No. 3,891,567 discloses aqueous compositions which contain from about 0.001 percent to about 10 percent of a particularly hydrolyzed polyacrylamide and about 0.001 percent to about 10 percent of a carboxyl vinyl polymer. These compositions are disclosed as a flooding medium for recovering oil from subterranean oil-bearing formations.
U.S. Pat. No. 3,679,000 discloses a process for tertiary oil recovery which comprises injecting viscous water into the area of the oil deposit through an input well by incorporating into the water a minor amount of a water soluble polymer containing 5 percent of a repeating unit of the formula: ##STR1## wherein R.sub.1 is a hydrogen or lower alkyl, R.sub.2 is a divalent or trivalent hydrocarbon, M is hydrogen or one equivalent of a cation, and X is one or two.
U.S. Pat. No. 4,148,746 discloses aqueous gels suitable as water thickening agents and are useful for enhanced oil recovery. This water thickening gel is prepared by polymerizing at least one alkyl acrylate monomer and at least one carboxylic polymerizable monomer selected from the group consisting of acrylic acid and methylacrylic acid. The carboxylic polymerizable monomer is present from 20 to 95 parts per weight per 100 parts of total monomer being polymerized and utilizing. The composition is disclosed as comprised of an emulsifier selected from the group consisting of disodium or diammonium nonylphenoxy polyethoxy sulfosuccinate having the general formula: EQU CH.sub.3 (CH.sub.2).sub.8 C.sub.6 H.sub.4 O(CH.sub.2 CH.sub.2 O).sub.8-16 COCH.sub.2 CH(COOM)SO.sub.3 Q
wherein Q is sodium or ammonium and a sodium or ammonium lauryl polyethoxysulfate having the general formula: EQU CH.sub.2 (CH.sub.2).sub.11 O(CH.sub.2 CH.sub.2 O).sub.8-16 SO.sub.3 Q
wherein Q is sodium or ammonium, the polymer is in a latex form which is neutralized to a pH ranging between a pH of 5.5 to 11.5. These polymers also may be gelled with a water soluble polyvalent compound such as sodium dichromate and a water soluble reducing agent such as sodium hydrosulfite.
It should be evident that there are numerous types of polymers useful for increasing the viscosity of water. Since water is the cheapest fluid for enhanced oil recovery, it is desirable to produce an aqueous composition containing the lowest cost polymers for enhanced oil recovery operations. Some of the previously known polymers such as those comprising acrylamide, can significantly increase the cost of aqueous compositions compared to other types of polymer systems.
Besides low cost polymers the cost of using polymers for increasing the viscosity of water may be reduced by preparing aqueous polymeric compositions, such as latexes, with a high solids percentage of the polymer in the composition. These concentrated polymer compositions are typically transported to the well site and admixed with water, with the mixture injected into the formation. A high solids-containing emulsion or latex reduces the cost of operation because of the reduced cost of transporting the composition to the well site. Aqueous polymer compositions, such as those disclosed in U.S. Pat. No. 4,148,746, typically have solid contents around 20 percent.
It should be noted that, while it is desirable to increase the weight percent of polymer in the composition the stability of the composition during preparation, storage, transportation, and/or use in enhanced oil recovery should be such that the polymer does not precipitate out of solution and thus create the potential for plugging the subterranean formation.
It can thus be seen that it would be desirable to provide a stable aqueous composition containing a high percent solids level of an inexpensive polymer capable of increasing the viscosity of water used for enhanced oil recovery.